Adipaldehyde is a valuable intermediate which is useful, for example, in the production of e-caprolactone by the Tischenko reaction, in the production of adipic acid by oxidation and in the production of 1,6-hexanediol by hydrogenation. Adipic acid and 1,6-hexanediol are also produced from other intermediates (e.g., adipic acid is also produced from cyclohexanone by oxidation. Adipaldehyde itself is produced by circuitous routes such as by the ozonolysis of cyclohexane. The processes currently used to produce adipaldehyde, e-caprolactone, adipic acid and 1,6-hexanediol have various disadvantages. For example, the oxidation reactions may involve the use of nitric acid which can produce nitrous oxide which is an ozone scavenger and which, therefore, may contribute to the greenhouse effect. Moreover, starting materials currently used to produce adipaldehyde, adipic acid and 1,6-hexanediol are relatively expensive. Accordingly, it would be desirable to produce adipaldehyde from a relatively inexpensive starting material (e.g., butadiene) and by a process (e.g., hydroformylation) which does not have the disadvantages of prior art processes. However, prior art processes for producing adipaldehyde by the hydroformylation of butadiene have not been especially satisfactory. In particular, the selectivity to adipaldehyde in prior butadiene hydroformylation processes has been low. Such prior art hydroformylation processes are described below.
Various publications disclose the hydroformylation of butadiene with rhodium catalysts modified by secondary or tertiary, alkyl/aryl phosphines and phosphites to produce dialdehydes but the selectivity to adipaldehyde is less than 10% with most of the dialdehyde product being branched. The conditions used are typically rather severe such as pressures over 750 bar (i.e., pressures over 11,025 psi). Among such publications are: (1) Tetrahedron Letters, 1969, 32,2721-2723, "Dialdehydes by Hydroformylation of Conjugated Dienes"; (2) Chemike-Zeitung, 1975, 99, 452-458, "Hydroformylation of Conjugated Dienes. II Cobalt Carbonyl and Rhodium Carbonyl Catalyst Systems in Hydroformylation of 1,3-Dienes"; (3) Chemike-Zeitung, 1975, 99,485-492, "Hydroformylation of Conjugated Dienes. III. Reaction Products of a Hydroformylation of Conjugated Dienes with Rhodium Carbonyl/tert-Phosphine Catalyst Systems"; (4) Journal of Molecular Catalysis, 1977,2,211-218, "The Hydroformylation of Conjugated Dienes V. Aliphatic Tertiary Phosphines and P-Substituted Phospholanes as Co-Catalysts of the Rhodium-Catalyzed Hydroformylation of 1,3-Dienes"; and (5) Symp. Rhodium Homogeneous Catalysis, 1978, 87-93. "Diols by Hydroformylation of Conjugated Dienes"; and (6) Journal of Molecular Catalysis, 1980, 8, 329-337, "The Hydroformylation of Conjugated Dienes. VI Tertiary Aryl- and Arylalkylphosphines and Secondary Aryl- and Alkylphosphines as Ligands in the Rhodium Catalyzed Hydroformylation Reaction of Conjugated Dienes to Dialdehydes". Publication (5) above describes conducting the hydroformylation in methanol solvent to form aldehyde acetals but the selectivity to adipaldehyde acetal was still less than 10%.
Other publication describe the hydroformylation of butadiene by rhodium catalysts modified with bidentate (i.e., diphosphorus) phosphine (diphosphine) ligands. No mention of phosphite or bis-phosphite ligands is made in these publications and the major product in each case is a saturated monoaldehyde. These publications are: (a) Journal of Organometallic Chemistry, 1980, 184, C17-C19, "Optically Active Aldehydes via Hydroformylation of 1,3-Dienes with Chiral Diphosphinerhodium Complexes"; (b) European Patent 33/554 A2, "A Process For the Hydroformylation of Conjugated Dienes"; and (c) Journal of Molecular Catalysis, 1985, 31, 345-353, "The Hydroformylation of Butadiene Catalyzed by Rhodium-Diphosphine Complexes". Publication (b) above discloses the use of such catalysts to produce valeraldehyde and to minimize the production of dialdehydes. Publication (c) above discloses that butadiene complexes with rhodium thus blocking its activity in heptene-1 hydroformylation.
European patent application 309,056 discloses the hydroformylation of V-olefins or V,l-diolefins with rhodium catalysts modified by bis(phosphinoalkyl)ether ligands, (R.sub.2 PCH.sub.2 CH.sub.2).sub.2 O. No mention of phosphite or poly-phosphite ligands or of butadiene reactants is made in that patent application.
U.S. Pat. No. 4,507,508 discloses a process for the hydroformylation of butadiene and other conjugated diolefins using a rhodium catalyst modified by a tertiary phosphine or phosphite ligand in the presence of an alcohol and a strong acid. The phosphites have alkyl, aryl, aralkyl or alkaryl groups containing from 10 to 30 carbon atoms and the alcohols contain from 1 to 4 carbon atoms. No mention of bidentate phosphites (bis-phosphites) is made. All the Examples in this patent use triphenylphosphine as the ligand and there is no Example using a phosphite ligand. Selectivities to dialdehydes of up to 80% are achieved, but the nature of the dialdehydes, whether branched or linear, is not specified. Based on other publications showing the use of phosphine ligands (i.e., Chem. Zeit 1975 99 485; ibid. 1975 99 452; J Mol Cat 1980 329; ibid. 1977 2 211; and Tet Lett 1969 32 ibid 2721), the dialdehydes produced in U.S. Pat. No. 4,507,508 were probably branched.
U.S. Pat. No. 3,947,503 discloses a two-step process for the hydroformylation of butadiene. In the first step, butadiene is hydroformylated using a rhodium catalyst modified by a tertiary phosphine or phosphite in the presence of an alkanol or alkanediol to produced an acetal of 3-pentene-1-al. The hydroformylation in the first step is said to occur at 50-600 atmospheres pressure (700-9000 psi). In the second step, the acetal is hydroformylated using a cobalt catalyst modified by a tertiary phosphine to produce dialdehyde acetal. The use of a cobalt catalyst in the second step is stated in the patent to be crucial in order to obtain a linear dialdehyde acetal. The dialdehyde acetal is then hydrogenated to 1,6-hexanediol. Up to 50% isolated yields (based on butadiene) are reported. The patent contains only one Example and in it a phosphine ligand is used. Poly-phosphites are not mentioned in this patent.
U.S. Pat. No. 4,769,498 discloses poly-phosphites and their use as ligands in rhodium-catalyzed olefin hydroformylation. The olefins to be hydroformylated are broadly described in this patent as: "terminally or internally unsaturated and of straight chain, branched chain, or cyclic structure. Such olefins can contain from 2 to 20 carbon atoms and may contain one or more ethylenic unsaturated groups". The patent names several specific mono-olefin reactants and two specific non-conjugated diolefin reactants (i.e., 1,4-hexadiene and 1,7-octadiene). Conjugated diolefins such as butadiene, which often considered special cases in hydroformylation reactions (see Chem. Zeit. 1975 99, 452; ibid. 1975 99 485; and J. Falbe "New Syntheses with Carbon Monoxide" Springer-Verlag NY, 1980, Pages 103-105), are not specifically disclosed in this patent and no Examples showing the hydroformylation of any butadiene are included.
U.S. Pat. No. 4,599,206 discloses the use of diorgano phosphite ligands in the rhodium-catalyzed hydroformylation of olefins. The disclosure of olefins in this patent is similar to the disclosure of olefins in U.S. Pat. No. 4,769,498 discussed above. That is, there is no specific disclosure of the hydroformylation of any butadiene.
U.S. Pat. No. 4,742,178 discloses the low-pressure (15-800 psi) hydroformylation of dienes containing 6 to 10 carbon atoms with a catalyst consisting of rhodium and various chelating diphosphine ligands containing certain biphenyl bridging groups. Examples using other chelating diphosphines are included for comparison. The hydroformylation of 1,7-octadiene to produce 1,10-decanedialdehyde in high conversion and selectivity is disclosed in the Examples and 1,7-octadiene is the only diolefin used in the Examples of this patent. This patent illustrates the relative ease with which non-conjugated dienes can be converted to alkanedials by prior art processes. However, no mention is made of hydroformylation of any butadiene or of catalysts containing mono-phosphites or poly-phosphites.
U.S. Pat. No. 4,808,756 discloses the hydroformylation of V,l-diolefins containing from 6 to 10 carbon atoms or V,l-alkenals containing from 7 to 10 carbon atoms with a catalyst consisting of rhodium and a monodentate sulfonated or carboxylated phosphine in an aqueous solution of sulfolane and extraction of the reaction mixture with an alcohol or hydrocarbon. The Examples show the hydroformylation of 7-octene-1-al, 1,7-octadiene, 1,5-hexadiene, or 1,9-decadiene. There is no disclosure of the hydroformylation of butadienes or of the use of mono-phosphite or poly-phosphite ligands.
U.S. Pat. No. 4,248,802 discloses the hydroformylation of olefins with a catalyst consisting of a rhodium-containing aqueous solution of certain sulfonated triaryl phosphine ligands. Phosphite and poly-phosphite ligands are not disclosed. Example 24 of this patent discloses the hydroformylation of butadiene at 80.degree. and 735 psi for 17 hours to give 75% C.sub.5 aldehydes, with only a trace of C.sub.6 dialdehydes.
Accordingly, it is an object of the present invention to provide a process for producing 1,6-hexanedials (e.g., adipaldehyde) by the hydroformylation of butadienes characterized by improved selectivity for the production of the 1,6-hexanedials.